The present invention relates to a novel method of mechano-chemically treating a material which enables:
on the one hand, improving, in one sole operation leading to a subsequent mechano-chemical anchoring, the surface properties of a material, such as, in particular, its aptitude to adherence during subsequent assemblings;
on the other hand, improving the surface properties of use of a material by the simple carrying out of a coating having composite structures.
This invention finds a first series of applications in every field in which it is sought to improve the interface properties of a material with a view to its use with another material, in particular during assemblings, notably during sticking together of the two materials, or during the adhesive filling of cavities.
The principal fields concerned are odontology, the biomedical field, the preparation of carried products which use microtechniques, the field of the automobile industry, and that of the avionics industry.
Within this context, the invention more particularly applies to the treatment of metallic pieces with a view to improving the coherence and the reactivity of the interface between the metal and a polymer material generally constituting glue or the coating intended to be applied thereon.
This invention finds a second series of applications in every field in which it is sought to improve the surface properties of use of a material, in particular of a material covered with a polymer, by the incorporation in this covering of fillers which are notably ceramic fillers, mineral or metallic fillers, by thus preparing composite structures the polymer covering of which constitutes the matrix.
Within this context, the invention applies more particularly to the preparation of hard non-adhesive (anti-adhesive) coverings.
The principal fields concerned are the printing industries, (textile or paper), those of agri-foodstuffs, the mechanical industries, with applications in the automobile industry.
At present, in every operation of preparation of a surface with a view to its assemblage by sticking with another surface, one proceeds in a classical manner sequentially by carrying out successively:
a mechanical treatment, by impacts of particles so as to generate a roughness intended to favour the mechanical anchoring;
and then, a chemical treatment, by successive applications, notably by daubing onto the surface, or by pulverising onto the surface thus mechanically treated, various chemical products intended to improve the properties of adhesion and of adherence of this surface.
The mechanical methods of surface treatment which are the most frequently carried out in industry or in laboratories, such as, for example, sandblasting, shot blasting, balling, etc., are based on projecting various projectiles onto the surface to be treated preferably projectiles of abrasive character. All these methods give good results while being easy to use.
The projectiles which can be used in the context of the methods mentioned above are of various nature and are generally characterised by their nature, their shape, their dimensions, their particle size, their density, their integrity.
Industrially, the most commonly used projectile is spherical or angular steel shot, round or angular cast iron shot, aluminium or copper shot, glass microballs, shot of ceramic material of the alumina or silica type.
In micro-sandblasting, for the moment, alumina or corundum grains are most frequently employed. These grains possess active ridges which guarantee a high efficiency in terms of macro- and micro-roughness of a surface.
In the particular field of odontology in which numerous operations of assembling are carried out by sticking together a metallic material and a polymer material, essentially two methods are known which aim to improve the quality of metal-polymer interfaces. These are:
on the one hand, a method developed by the company ESPE and known under the designation  less than  less than Rocatec(copyright) method greater than  greater than ; and
on the other, a method developed by the company KULZER and known under the designation  less than  less than Silicoater MD(copyright) method greater than  greater than .
The Rocatec(copyright) method enables carrying out a sandblasting qualified as a  less than  less than reactive greater than  greater than  sandblasting. This method starts off with a first sandblasting by alumina grains of about 250 xcexcm, which is followed by a second sandblasting which uses alumina grains of size which is roughly equal to that of the preceding ones but which are covered in silica micro-grains. These two types of sandblasting are followed by a step of brush-depositing a layer of silane.
This method, which comprises three steps, necessitates the purchase of a specific sandblasting unit.
The Silicoater MD(copyright) method consists essentially in carrying out a deposit of silica onto the metallic surfaces by pyrolysis. This method, which does not comprise any sandblasting operation, does nevertheless necessitate a specific piece of equipment, and in particular a heating enclosure.
Thus, the methods of surface treatment which are classically used up to present with a view to carrying out a cohesive assembling necessitate the use of specific pieces of equipment and/or are generally carried out sequentially, and this manifests itself by the relatively significant latent periods between the mechanical and chemical treatments, even between various successive chemical operations, which risk disturbing the quality of the expected results.
It is in this context that the inventors have sought developing a method of treating a material which does not necessitate any specific piece of equipment and which notably enables improving the surface properties of this material, in one sole step, during which a mechanical treatment by impacts and a chemical treatment were carried out concomitantly, or enables improving the properties of use of this material by preparing a surface covering of composite structures.
The method developed in accordance with the present invention in order to attain this objective is essentially characterised by the fact that it comprises projecting onto a material particles having stratified structure which are constituted of a core and of a coating comprising at least one polymer and optionally a chemical agent, under conditions such that said particles and/or the fragments resulting from their fracturing become encrusted in and/or penetrate into said material.
According to a first embodiment, this method is intended to improve the surface properties of a material, and in particular its adherence during its assembling with a second material, and comprises projecting particles having stratified structure onto the surface of said material, under conditions such that said particles fragment during impact and become encrusted in said material.
An anchoring is thus obtained in one sole operation, at the surface of the material to be treated, of fragments of projected particles, and, consequently, an anchoring of their coating is thus obtained, this operation being designated in the present application by the expression xe2x80x9cmechano-chemical anchoringxe2x80x9d.
In other words, the chemical reaction on the surface of the treated material is linked to a concomitant encrustation of the stratum or strata of the stratified particles, this encrustation improving the interfacial adhesion.
More generally, the expression xe2x80x9cmechano-chemicalxe2x80x9d is understood as describing any operation which simultaneously comprises a mechanical component and a chemical component.
In this aspect, the present invention therefore enables carrying out, without any latent period between the various operations, a surface treatment of a material which groups together mechanical operations and chemical operations which are linked to the reactivity of the interfaces, and this provides a more particular advantage with respect to the treatments of the prior art which are always sequential.
Another advantage of this method resides in the fact that it does not necessitate any specific material for its implementation, it being possible for this implementation to be carried out with the aid of apparatuses which are classically used for mechanical operations of sandblasting, micro-sandblasting, shot blasting, or balling.
This method enables, inter alia, the preparation of a surface, in particular of a metallic surface, onto which it is desired to adhere or to join a different material, in particular a polymer material.
Many materials can be treated within the context of this method. Metallic materials, ceramics, polymers, as well as calcified materials will be cited in particular.
According to a particular characteristic of this method, particles having stratified structure the core of which is constituted of a grain or of a ball made from a intrinsically fragile material, such as, for example, a ceramic, in particular from alumina, or from silica, or from a material having a natural aptitude to fragment under impacts of imposed energy, such as, in particular, a steel ball, a cast iron ball or a glass ball, will be used as projectiles.
The core of the particles having stratified structure can even be made from a plastic material, or from a traditional sandblasting material such as kaolin or refractory materials.
According to another particular characteristic, in the case in which the second assembling material is a polymer, particles having stratified structure the coating of which comprises one or more strata comprising a polymer of chemical family which is analogous to that of said polymer constituting the second assembling material, will be used as projectiles.
According to a second embodiment, the method in accordance with the present invention is intended to improve the properties of use of a material, by carrying out coverings having composite structures and in this case, the projection of the particles having stratified structure will be carried out under conditions such that said particles fully penetrate into said material without significantly fragmenting.
This embodiment of the invention is particularly useful for treating a polymer material, such as, in particular, for covering a mono- or multi-layered structure.
Polytetrafluoroethylenes (teflon), silicones (vulcanising at ambient temperature or at high temperature) or polyurethanes, can be cited amongst the polymers which can be thus treated.
Other materials can be treated in the context of this method. Biomaterials will be cited in particular.
According to a particular characteristic of this method, particles having stratified structure the core of which is constituted of a grain or of a ball made from a ceramic material, from a metallic material, from a plastic material or even from a traditional sandblasting material such as kaolin or refractory materials, will be used as projectiles.
Materials such as carbides, nitrides, oxides, carbonitrides or mixtures of these compounds can be cited, such as, for example, ceramic materials constituting the core of the projectiles.
Materials based on copper, on aluminium or on transition metals of the 3d or 4f series can be cited, such as, for example, metallic materials constituting the core of the projectiles.
Alloys of these metals are also envisagable.
According to a particular characteristic, in the case in which the material to be treated forms a polymer covering of a mono- or multi-layered structure, particles having stratified structure the coating of which comprises one or more strata comprising a polymer of the same chemical nature as a stratum of said covering, will be used as projectiles.
The person skilled in the art will easily understand upon reading the present description that it will be necessary for the nature and the dimensions of the particles having stratified structure, the nature of the material to be treated, as well as the conditions of the projection of said particles (their speed in particular) to be selected as a function of the surface properties or properties of use sought after.
For example, in the case of a surface treatment with a view to a sticking together, the person skilled in the art will select these various parameters in such a way that:
the size and the hardness of the particles having stratified structure be sufficient in order to create a surface roughness which favours the mechanical anchoring,
the constituents of the particles having stratified structure be able to rupture under impact, in such a way that, after fracturations or cracks, an encrustation of a fragment of the particle and of a part of the layer(s) of coating material be able to be observed on the surface of the material to be treated.
For a further example, in the case of a treatment intended to carry out a composite covering, the person skilled in the art will select the nature of the particles having stratified structure, and will regulate the speed of projection in such a way that said particles be able to penetrate inside the material to be treated, without fragmenting.
Generally, whatever the result sought after, particles the dimensions of which are between 0.1 xcexcm and 6 mm, preferably between 10 xcexcm and 500 xcexcm, will advantageously be selected.
It will be possible for the particles having stratified structure used within the context of the invention to be prepared by methods classically used for sugar-coating of particular products, and in particular by techniques of pulverisation in a fluidised gaseous bed, or by techniques of polymerisation in suspension, commonly used in microencapsulation.
Coating by pulverisation in a fluidised gaseous bed is perfectly systematised. The objective being to maintain the pulverulent products in suspension in the zone in which the encapsulating product is pulverised, so as to obtain a total coating of the particles.
If M is the mass of pulverulant solid product to be sugar-coated, and if m is the total mass of liquid products pulverised in order to carry out this operation, the theoretical encapsulation rate is provided by the formula:       m          M      +      m        xc3x97  100.
Generally, a rate of 10 to 20% is observed and procures the results sought after.
The efficiency of the encapsulation is generally verified on the Sweeping Electron Microscopy (SEM) scale.
The technique of pulverisation in a fluidised air bed favours the preparation of large amounts of products and applies particularly well to particles the size of which is between 50 xcexcm and 4 mm.
This technique can be used in a sequential manner in order to deposit successive strata in the case of a multi-layered coating of the stratified particles.
Another method exists which enables creating real chemical bonds between the various strata, or between the core and the stratum immediately adjacent.
A polymerisation reaction can be carried out in order to favour the anchoring of the first stratum with the material selected for carrying out a second, peripheral stratum.
It will be possible for the system to be reproduced in a recurrent manner provided that there be in this case chemical bonds between the penultimate layers.
This technique will advantageously be selected for particles of low size (xe2x89xa650 xcexcm) and advantageously for particles of size of the order of 0.5 xcexcm.
It will be possible for the particles having stratified structure to be projected by means of projection devices which are usually used in surface treatment methods, especially compressed air or turbine devices.
The person skilled in the art will easily determine the implementation conditions of these devices and in particular the speed of projection of the particles, as a function of the objective sought after (surface treatment or preparation of a composite covering).
In the particular case of a surface treatment, it will be possible for the particles to be projected in the presence of a liquid carrier which is preferably constituted of water or of an aqueous solution.
According to a particular characteristic of the invention, and whatever the embodiment envisaged, it will be possible for the coating to comprise at least two strata, the stratum immediately in contact with the core of the particle optionally comprising a chemical agent intended to increase the adherence between said stratum and said core, or between said strata.
More generally, it will be possible for the coating to be constituted of a single stratum or of a plurality of strata and it will be possible for each stratum to comprise one or more chemical agents such as products known as adhesion promoters or an as adhesion primers.
In this context,  less than  less than adhesion promoter greater than  greater than  is understood as meaning any substance which enables modifying the chemical nature of a surface in order to optimise the adhesion with another surface, and  less than  less than adhesion primer greater than  greater than  is understood to mean any substance which enables facilitating the adhesion and the adherence of an adhesive.
Compounds which are generally designated in the field by the term  less than  less than silanes greater than  greater than  will be cited as examples of an adhesion promoter. These are bifunctional molecules which are capable of exchanging bonds with two different materials and one of which is a mineral. Thus, alkoxysilanes are advantageous insofar as:
certain functions of the silane can condense, when such is the case, with the hydroxyl groups borne by the surfaces of the element constituting the core of the composite particles, in order to form Sixe2x80x94O-metal bonds,
it will be possible for the alkyl(acrylic or methacrylic) groups of the silane to subsequently polymerise, if need be with the monomers constituting the next coating layer. This is the case in particular when the composite particle comprises a first layer of alkoxysilane and a second layer, called peripheral layer, which is constituted of an acrylic polymer.
According to a variant, the particles having stratified structure will comprise an external layer or stratum which contains an adhesion primer and an underlying layer or stratum which contains an adhesion promoter.
Such particles constitute novel industrial products per se.
Of course, the choice of both the adhesion promoter and the adhesion primer will depend upon the nature of the element constituting the core of the composite particles and upon the objective sought after during the implementation of the method.
Thus, in a particular case in which it is sought to carry out a composite covering, it is generally advantageous to use as projectiles particles comprising one or more strata and the stratum of which immediately in contact with the core is fixed thereon by chemical bonds.
In the particular case in which it is sought to assemble two materials, by sticking together by means of an acrylic glue, composite particles will be selected the coating of which will be constituted or will comprise an acrylic compound the formulation of which will be close to that of the material forming the glue.